This invention relates to semiconductor heterostructure devices, such as double heterostructure (DH) junction lasers, and to liquid phase epitaxy (LPE) growth techniques for fabricating such devices.
An active device such as a GaAs-AlGaAs DH junction laser and passive device such as a waveguide are typically similar in composition and impurity doping. However, it is difficult as a practical matter to physically join such active and passive devices together in an integrated circuit with suitable isolation because the laser radiation which is emitted at energies near the GaAs bandgap is highly attenuated in a passive waveguide of identical composition. In order to transmit the radiation emanating from a GaAs LED or DH laser, the light guiding layer of the waveguide must be transparent to the generated light. That is, the light guiding layer should be constructed out of a semiconductor with a higher effective bandgap than GaAs. In practice this requirement means that the active region in the GaAs laser should change relatively abruptly to AlGaAs at the active-to-passive interface, but not so abruptly that significant reflections occur at the interface due to impedance mismatch.